This invention relates to a method of preparing modified starch products, and, particularly, to stabilized starch products containing phosphorus and nitrogen.
While various methods of chemically modifying starch to produce modified starch products containing phosphorus have been proposed and are described in the literature, many of these methods involve dry reaction procedures. Such methods consist, for the most part, of impregnating the dry starch base with a phosphorus containing reagent solution which has a pH within a prescribed range and then heating the thusly treated starch to a particular temperature and holding it at such temperature for a certain period. For example, a representative method of the prior art for phosphorylating starch would involve impregnating starch with sodium dihydrogen phosphate (in an amount of from 2% to 4% by weight of the dry starch), at pH 4 - 8, drying the starch and heating at 120 - 130.degree. C. for one to three hours.
Starch reactions which are carried out in aqueous media are, from a large-scale production viewpoint, more economical. However, both the wet and dry processes of the prior art are limited in the type of substituent groups with which a starch base can be modified.
It is an object of this invention to provide an efficient and economical method for preparing chemically modified starches which are characterized by their greater stability, their ability to form clearer cooked pastes which are more resistant to gelling upon cooling, and their lowered gelatinization temperatures, as compared to the corresponding untreated starches. Another object of this invention is to provide a new method for preparing starch derivatives which contain phosphorus and nitrogen groups, i.e. phosphoramidic acid groups. A further object of this invention is to provide starches modified by functional groups not heretofore used in the modification of starches by the known methods.